Active Damping During Clutch Engagement for Engine Start

ABSTRACT

An active damping system provides a torque adjustment command that is combined with the raw motor torque command of a vehicle to compensate for oscillations and vibrations in the driveline of a hybrid vehicle. Active damping may be provided by a derivative controller or by a lead-lag compensation between initiation of clutch engagement and full clutch engagement. Active damping is terminated upon full clutch engagement.

TECHNICAL FIELD

This disclosure relates to suppressing driveline oscillations in amodular hybrid vehicle by adjusting the torque command to the electricmachine of the hybrid vehicle.

BACKGROUND

Hybrid vehicle architecture may take several forms for operativelyconnecting a battery, an electric traction motor and a combustion enginetogether in the driveline of the vehicle. One proposed architecture indevelopment by the assignee of this application is a Modular HybridTransmission (MHT). One embodiment of the MHT is the ElectricConverter-Less Transmission (ECLT). To replicate the torque converterfunction of a conventional automatic transmission, the MHT powertrainwithout a torque converter may rely upon active controls of astarter/alternator and a disconnect clutch between the combustion engineand the electric motor. Alternatively, the MHT may also be provided witha torque converter. A launch clutch or torque converter may be providedbetween the electric motor and the wheels.

The drivability of the MHT must be comparable to drivelines having aproduction automatic transmission. A major control challenge of the MHTis to absorb “clunks,” pulsations and vibrations in the driveline duringengine start and clutch engagement, creating a quieter, less stressfuldriving experience.

New challenges arise with MHT systems as to the coordination of theclutch, engine and motor, especially during the complicated clutchengagement transients. All the friction element control, pressurecontrol, and the motor toque control should be integrated seamlessly todeliver smooth wheel torque. In addition, converter-less disconnectclutch engagement is very sensitive to the clutch pressure and it is achallenge to achieve the proper damping and smoothness during the clutchengagement.

The engine in a MHT must start smoothly and quickly. Every start isaccompanied by a transient clutch engagement phase during which timesubstantial inertial drag and torque disturbances are transferred to thedriveline. The difficulty and uncertainty of estimating the engine andclutch torque caused by complicated transient dynamics are a challengingtask for motor torque compensation.

During the MHT clutch engagement transient for engine starts, there areproblems of oscillations arising from the excitation of the mechanicalresonance by various disturbances. This resultant oscillation phenomenonis due to low damping in the driveline due to the absence of a torqueconverter. Applying the electric motor torque generates torque rippleswith frequencies that are motor speed dependent.

The above problems and other problems are addressed by the presentdisclosure as summarized below.

SUMMARY

An active damping strategy is proposed that allows for the improvementof the dynamic response and rejection of the driveline oscillations byadjusting the electric motor torque command during disconnect clutchengagement. Active damping is terminated when the disconnect clutch isfully engaged when active damping is terminated. Motor torque adjustmentfor active damping is based on the processing speed measurementsobtained from the motor speed or wheel speed sensor. The active dampingsystem adjusts the electric motor torque command to damp oscillations inthe driveline.

According to one aspect of the disclosure, a hybrid vehicle is providedthat comprises an electric machine, an engine and a battery forsupplying power to the electric machine and a controller. The controlleris configured to provide a base motor torque command, detect a period ofclutch engagement after an engine start command is provided by thecontroller, and suppress a driveline oscillation during the period ofclutch engagement. Driveline oscillations are suppressed by an activedamping algorithm that adjusts the magnitude of the torque commandedfrom the motor by modifying the base motor torque command.

According to another aspect of the disclosure a method is provided foroperating a hybrid vehicle having an engine that is selectivelyconnected to a driveline by a disconnect clutch and a secondary powersource. The method comprises obtaining a base motor torque command,detecting a period of clutch engagement after an engine start commandthat ends upon full clutch engagement, and attenuating oscillations inthe driveline by providing an active damping torque adjustment to thebase motor torque command.

According to other aspects of both the vehicle and the method, thesuppression of driveline oscillation may be performed based upon aderivative controller that receives an input signal representative of aspeed of rotation of a driveline component. The speed of rotation of thedriveline component may be a motor speed signal or a wheel speed signal.

The derivative controller has the following transfer function in thes-domaine: G=ks where s is the Laplace transform variable k=gain.

Alternatively, the suppression of the driveline oscillation may beperformed based upon a lead-lag compensator controller. The lead-lagcompensator has the following transfer function in the s-domain:G=k(s+z)/(s+p), where: s is the Laplace transform variable; k=gain;z=zero; and p=pole.

According to other aspects of the disclosure, the disconnect clutch inthe driveline between the electric machine and the engine may beselectively provided with hydraulic pressure to disengage the disconnectclutch. The hydraulic pressure may be reduced to zero when the engine isoff, and the period of clutch engagement may be preceded by a timeboosting period in which the clutch is filled and the hydraulic pressureis set to a stroke pressure. Alternatively, hydraulic pressure may bemaintained at a stroke pressure when the engine is off. The disconnectclutch may be selectively provided with hydraulic pressure. If so, theperiod of clutch engagement may begin at the time of the engine startcommand.

These and other aspects of this disclosure will be more fully explainedwith reference to the attached drawings and the following detaileddescription of the illustrated embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a diagrammatic view of a modular hybrid transmission systemfor a hybrid vehicle that does not include a torque converter;

FIG. 1B is a diagrammatic view of an alternative embodiment of a modularhybrid transmission system for a hybrid vehicle that includes a torqueconverter;

FIG. 2 is a control diagram for an active damping system for attenuatingdriveline oscillations;

FIG. 3 is a control diagram for a transient clutch engagement detectionsystem; and

FIG. 4 is a graphical representation of an active damping system duringtransient clutch engagement.

DETAILED DESCRIPTION

A detailed description of the illustrated embodiments of the presentinvention is provided below. The disclosed embodiments are examples ofthe invention that may be embodied in various and alternative forms. Thefigures are not necessarily to scale. Some features may be exaggeratedor minimized to show details of particular components. The specificstructural and functional details disclosed in this application are notto be interpreted as limiting, but merely as a representative basis forteaching one skilled in the art how to practice the invention.

Referring to FIGS. 1A and 1B, a modular hybrid transmission 10 is shownin a diagrammatic form. A engine 12 is operatively connected to astarter 14 that is used to start the engine 12 when additional torque isneeded. A motor 16, or electric machine, is operatively connected to adriveline 18. A disconnect clutch 20 is provided on the driveline 18between the engine 12 and the electric machine 16. A transmission 22, orgear box, is also provided on the driveline 18. Torque transmitted fromthe engine 12 and motor 16 is provided the driveline 18 to thetransmission 22 that provides torque to the wheels 24. As shown in FIG.1A, launch clutch 26A is provided between the transmission 22 and theengine 12 and/or motor 16 to provide torque through the transmission 22to the wheels 24. As shown in FIG. 1B, a torque converter 26B isprovided between the transmission 22 and the engine 12 and/or motor 16to provide torque through the transmission 22 to the wheels 24. Whileelimination of the torque converter is an advantage of the embodiment ofFIG. 1A, the present disclosure is also advantageous in reducingvibrations in systems having a torque converter 26B like that shown inthe embodiment of FIG. 1B.

The vehicle includes a vehicle system control (VSC) for controllingvarious vehicle systems and subsystems and is generally represented byblock 27 in FIG. 1. The VSC 27 includes a plurality of interrelatedalgorithms which are distributed amongst a plurality of controllerswithin the vehicle. For example, the algorithms for controlling the MHTpowertrain are distributed between an engine control unit (ECU) 28 and atransmission control unit (TCU) 29. The ECU 28 is electrically connectedto the engine 12 for controlling the operation of the engine 12. The TCU29 is electrically connected to and controls the motor 16 and thetransmission 22. The ECU 28 and TCU 29 communicate with each other andother controllers (not shown) over a hardline vehicle connection using acommon bus protocol (e.g., CAN), according to one or more embodiments.Although the illustrated embodiment depicts the VSC 27 functionality forcontrolling the MHT powertrain as being contained within two controllers(ECU 28 and TCU 29) other embodiments of the HEV include a single VSCcontroller or more than two controllers for controlling the MHTpowertrain.

Referring to FIG. 2, one embodiment of an active damping system 30 isshown. The VSC 27 includes a torque control algorithm 30, or strategy,which controls the disconnect clutch 20 and launch clutch 26. Thecontrol algorithm 30 and clutches 20 and 26A (or torque converter 26B)permit the modular hybrid transmission 10 to obtain additional operatingefficiency. The control algorithm may be contained within the TCU 29according to one or more embodiments, or may be incorporated in hardwareor software control logic as described in detail below. A base motortorque determination strategy 32 is developed in a torque control systemwhich controls operation of the engine 12 and motor 16 (shown in FIG. 1)and provides a raw motor torque command output signal 36.

An absolute value speed signal 38 is provided to an active dampingcontrol routine 40. The absolute value speed signal 38 may be the motorspeed signal or a vehicle speed signal. The active damping controlroutine 40 is based upon processing a motor speed value or a wheel speedvalue that is obtained from a sensor. The active damping control routine40 produces a compensating torque to damp oscillatory modes of thedriveline 18 (shown in FIG. 1). A closed loop feedback control system isapplied to adjust the torque control to suppress driveline oscillations.In the closed loop system, a compensator is placed in the feedback paththat uses the motor speed or wheel speed as an input. The compensatoroutput, or delta motor torque signal 42, is provided to a block 44.

Part of the active damping system 30 includes a clutch engagementdetection routine 46. The clutch engagement detection routine 46 mayinclude inputs, such as a clutch pressure input 48, a rotational speedof the engine input 50 and a rotational speed of the motor input 52. Theclutch engagement detection routine processes the inputs and sets a flag54, as will be more specifically described with reference to FIG. 3below. The delta motor torque signal 42 is transmitted in the form of anactive damping motor torque signal 56 when the set flag condition issatisfied in block 44. The raw motor torque command 36 is adjusted bythe active damping motor torque signal 56 to provide the motor torquecommand signal 58 to the motor 16 (shown in FIG. 1).

Referring to FIG. 3, the clutch engagement detection routine 46 is shownin greater detail. The clutch engagement detection algorithm begins bystarting a timer in block 60. The system determines the time boostingvalue 62 based upon inputs including a hydraulic oil temperature input64 and a hydraulic line pressure input 66. Other signals may also beused to more closely approximate the time required to boost the clutchfluid pressure prior to beginning clutch engagement. The temperature 64and line pressure 66 are used to determine the time boosting factor insystems where, if fully disengaged, the clutch pressure is permitted tofall below a stroke pressure value to zero and thereby further improvesystem efficiency.

In systems where the stroke pressure is always maintained by thehydraulic pump that services the disconnect clutch 20 (as shown in FIGS.1A and 1B), the step of determining the time boosting factor may beomitted. However, in a system where time boosting is required tocompensate for delays actuated in the clutch, the time T correspondingto the start of the timer when the stroke pressure is applied at block60 is compared to the time boosting value at block 70. If the time T isless than the time boosting factor, the flag for clutch engagement isset to equal false at block 76. Alternatively, if the time T is not lessthan the time boosting factor at block 70, the algorithm proceeds toblock 72 to determine whether the clutch 20 is engaged by taking theabsolute value of the speed of rotation of the engine less than thespeed of rotation of the motor. If the absolute value is less than aspecified tolerance value, the flag is set to clutch engagement true atblock 74. When the flag is set at block 74, the delta motor torquesignal 42 is used to adjust the active damping motor torque signal 56.The delta motor torque signal 42 is combined with the raw motor torquecommand 36 to provide the desired motor torque command 58 that includesadjustments for active damping.

The engagement detection algorithm first detects the beginning of thecontact point at which the clutch force begins to drag the engine up toovercome engine inertia. The clutch travel distance and boosting time(Time_(boosting)) before the clutch transmits torque are approximatelypredictable and may be derived based upon a stored value table. Theduration of Time_(boosting) can be inferred from the line pressurecommand alone assuming that the impact of the temperature of thehydraulic oil is negligible. The relationship of Time_(boosting) andline pressure can be captured in a calibration table that may beconstrued empirically based upon clutch engagement experimentationtesting. The timing of the contact point may be inferred from the knownTime_(boosting) and known timing of the clutch pressure command. Theending point of the engagement where the clutch is fully engaged can bedetected by measuring the difference between the engine and motorspeeds. Clutch engagement is completed when the engine speed signal andmotor speed signal are equal or within a predetermined difference.

In systems where a minimum stroke pressure is provided by the hydraulicsystem of the clutch, clutch engagement detection may begin withapplication of the stroke pressure without requiring the calculation ofa Time_(boosting) timing factor. In such systems, the clutch engagementflag is immediately set upon application of the stroke pressure to theclutch and terminates when the engine and motor speeds are close enoughor equal as indicated previously.

Referring back to FIG. 2, the active damping closed loop control at 40may be provided by using a derivative controller on the feedback path.The derivative controller has the following transfer function ins-domain:

-   -   G=ks    -   where:    -   k=gain;    -   s is the Laplace transform variable.

The derivative control system places a compensator with the motor speed(or wheel speed) as its input in the feedback path into the motor torquecommand to attenuate oscillations.

Alternatively, the active damping closed loop control 40 may be providedby the a lead-lag compensator with the following transfer function ins-domain:

G=k(s+z)/(s+p)

-   -   where:    -   k=gain;    -   z=zero;    -   p=pole; and    -   s is the Laplace transform variable.

The above equation is a simple first order filter that is used toapproximate a derivative control. The z and p values are selectedaccording to the frequency that the closed loop system desires. Witheither the derivative control or lead-lag compensation, no additionalsensor is required since the motor speed or wheel speed sensor isalready provided for motor control or anti-lock braking system (ABS)control. Attenuation of disturbances at resonant frequencies can beobtained if the compensator and the gains are properly designed. Adesired frequency response from the torque command to the shaft torquecan be provided to the motor 16.

Referring to FIG. 4, an illustration of the active damping adjustment ofthe motor torque is illustrated. Referring to FIG. 4, top line 80illustrates the disconnect clutch pressure from a point at which theengine is not operational and the vehicle is being powered by theelectric motor. The disconnect clutch pressure in systems where thestoke pressure is permitted to drop to zero is presumed to be at zero. Astarter signal 82 indicates that in the initial period the starter isstopped, but upon initiation of engine operation, the starter motor isinitiated as indicated by the elevated portion of line 82. Upon initialstart-up, the clutch 20 fills with maximum pressure being provided tofill the clutch. Upon filling, the pressure within the clutch ispermitted to fall to a stoke pressure level just prior to the time thatthe clutch force begins to drag the engine. The engine speed, shown byline 84, is initially zero, but begins to increase shortly after theinitial starting command. At this point, the starter has started theengine and fuel is provided to the engine, whereupon the engine speedincreases as the result of the beginning of the combustion process. Theengine speed continues to increase until it reaches the motor speedindicated by line 86. Upon the engine speed 84 reaching the motor speed86, a determination is made that the clutch is fully engaged.

Referring to line 88, representing the motor torque, motor torqueremains relatively constant throughout the pre-starting and clutchengagement process. The engine torque, shown by line 90 is initiallynegative when the starter/motor begins providing starter torque as shownby line 92. Engine torque increases rapidly after the engine starts atwhich point torque is being provided by both the motor, as shown by line88, and by the engine, as shown by line 90. Transmission of enginetorque through the clutch is shown by line 94 which indicates thatinitially engine torque transmitted to the clutch is negative, but asthe engine torque increases, the engine torque transmitted to the clutchlikewise increases as shown by line 94. The continuing clutch engagementis shown by dotted line 96 in FIG. 4 and the clutch fully engagedcondition is indicated by the dotted line 98 in FIG. 4.

The delta motor torque line 100 illustrates the operation of the activedamping system to attenuate driveline oscillation. The delta motortorque signal is made available beginning when the clutch force beginsto drag the engine at the dotted line 96. Active damping whether underthe derivative control or lead-lag compensation approach provides abasis for adjusting the motor torque command 58, as shown in FIG. 2.Active damping continues until the clutch is fully engaged at dottedline 98. After the clutch is fully engaged, active damping is no longerrequired to attenuate oscillations caused by the engine start-up andclutch engagement.

While exemplary embodiments are described above, it is not intended thatthese embodiments describe all possible forms of the invention. Rather,the words used in the specification are words of description rather thanlimitation, and it is understood that various changes may be madewithout departing from the spirit and scope of the invention.Additionally, the features of various implementing embodiments may becombined to form further embodiments of the invention.

1. A hybrid vehicle comprising: a motor; an engine and a battery forsupplying power to the motor; a hydraulically actuated disconnect clutchselectively connects the motor and the engine; and at least onecontroller configured to modify motor torque based upon driveline speedduring a period of clutch engagement after an engine start to suppress adriveline oscillation during the period of clutch engagement, whereinthe motor torque is modified based upon a derivative controller thatreceives an input signal representative of a speed of rotation of adriveline component.
 2. (canceled)
 3. The hybrid vehicle of claim 1wherein the speed of rotation of the driveline component is a motorspeed signal.
 4. The hybrid vehicle of claim 1 wherein speed of rotationof the driveline component is a wheel speed signal.
 5. The hybridvehicle of claim 1 wherein the motor torque is calculated by thederivative controller in response to a motor speed input signal.
 6. Thehybrid vehicle of claim 1 wherein the motor torque is calculated by thederivative controller in response to a wheel speed input signal.
 7. Thehybrid vehicle of claim 1 wherein the motor torque is controlled basedupon a lead-lag compensator controller.
 8. The hybrid vehicle of claim 1wherein the hydraulic pressure is reduced to zero when the engine isoff, and wherein the period of clutch engagement is preceded by a timeboosting period in which the clutch is filled and the hydraulic pressureis set to a stroke pressure.
 9. The hybrid vehicle of claim 1 whereinthe disconnect clutch is selectively provided with hydraulic pressure toactuate the disconnect clutch, wherein the hydraulic pressure ismaintained at a stroke pressure when the engine is off, and wherein theperiod of clutch engagement begins with the engine start.
 10. A methodof operating a hybrid vehicle having an engine that is selectivelyconnected to a driveline by a disconnect clutch that is selectivelyactuated by hydraulic pressure and a motor comprising: during a periodof clutch engagement after an engine start that ends upon full clutchengagement attenuating oscillations in the driveline by modifying motortorque, and wherein attenuating oscillations in the driveline isperformed based upon a derivative controller that receives an inputindicative of a driveline component speed.
 11. (canceled)
 12. The methodof claim 10 wherein the driveline component speed is a motor speedsignal.
 13. The method of claim 12 wherein motor torque is controlled bya derivative controller that receives the motor speed signal.
 14. Themethod of claim 10 wherein the driveline component speed is a wheelspeed signal.
 15. The method of claim 14 wherein the motor torque iscontrolled by a derivative controller that receives the wheel speedsignal.
 16. The method of claim 10 wherein attenuating oscillations inthe driveline is performed based upon a lead-lag compensator controller.17. The method of claim 10 wherein the disconnect clutch is selectivelyprovided with hydraulic pressure to connect or disconnect the disconnectclutch, wherein the hydraulic pressure is reduced to zero when theengine is off, and wherein the period of clutch engagement is precededby a time boosting period in which the clutch is filled and thehydraulic pressure is set to a stroke pressure.